Lithium ion secondary batteries, which are nonaqueous electrolyte batteries, are in widespread use by introducing the batteries to electronic devices such as smartphones and laptop type personal computers, and vehicles such as hybrid cars, plug-in hybrid cars and electric cars. The lithium ion secondary battery can be produced, for example, by putting an electrode group, which is obtained by laminating a positive electrode and a negative electrode via a separator sandwiched therebetween, or by spirally winding the laminate formed in this way, in a container including aluminum or aluminum alloy as a material, and injecting an electrolyte solution, which is prepared by dissolving an electrolyte salt including lithium in a nonaqueous solvent, into the container.
Issues related to lithium ion secondary batteries include increasing a capacity and prolonging the life thereof, and it has been desired for such batteries to have a large capacity and exhibit good charge-and-discharge cycle characteristics.
One of the measures for increasing the capacity of the lithium ion secondary battery is to use a lithium-nickel composite oxide as a positive electrode active material. The lithium-nickel composite oxide, however, easily causes a side reaction on an electrode, and has a defect by which the capacity thereof may possibly be reduced when the cycle is repeated.